A perpendicular magnetic recording head includes a main magnetic pole (for example, a main magnetic pole (35) described in Patent Document 1) and a return yoke layer (for example, a sub-magnetic pole (34) described in Patent Document 1), and a coil layer (for example, an excitation coil (36) described in Patent Document 1) as described in patent documents described below.
For example, FIG. 5 of Patent Document 1 is a front view of each magnetic layer as viewed from the opposed surface of a recording medium. As shown in FIG. 5 of Patent Document 1, the area in the opposed surface of the main magnetic pole layer is even smaller than the area in the opposed surface of the return yoke layer. As a result, a leakage recording magnetic field is concentrated on a front end of the main magnetic pole layer and the recording media is perpendicularly magnetized by the concentrated magnetic flux. Therefore, magnetic data is recorded. The magnetic flux returns to the return yoke layer after passing through the recording medium.
[Patent Document 1] JP-A-2002-100006 (US2002036871A1)
[Patent Document 2] JP-A-2005190515 (US2005141142A1)
[Patent Document 1] JP-A-2004-342164 (US2004228030A1)
However, when the temperature in the perpendicular magnetic recording head rises at the time of a recording operation, the return yoke layer, occupying a formation region still larger than other parts, easily is projected from the opposed surface. This is due to the difference in a thermal expansion coefficient from an insulating material in the vicinity of the return yoke layer. Consequently, a phenomenon called PTP (Pole Tip Protrusion) is generated.
Accordingly, thickness of the return yoke layer may be thinned to suppress the PTP.
However, if the thickness of the return yoke layer is thinned and the area of the return yoke layer exposed to the opposed surface becomes smaller, the return hole of the magnetic flux generated in the main magnetic pole layer becomes smaller. Particularly, the vicinity of a region opposed to the main magnetic pole layer in a film thickness direction easily reaches magnetic saturation, thereby reducing a recording ability.
The patent documents described above do not disclose the problems of generation of PTP and the reduction of the recording ability. Accordingly, the patent documents do not disclose solutions for suppressing the generation of the PTP and avoiding reduction of the recording ability.
Patent Document 3 described above relates to a shield layer used in the perpendicular magnetic recording head and discloses the invention in which a convex portion is provided toward the main magnetic pole layer. As a result, it is possible to remedy the curvature of a magnetization reversal form of a recording bit cell. (Paragraph [0032] of Patent Document 3).
However, Patent Document 3 discloses the invention relating to the shield layer as described above. In Patent Document 3, the shape of the return yoke layer is not improved. If the shield layer serves as the return yoke layer, the convex portion can protrude to the main magnetic pole layer. Accordingly, because the magnetic flux, which returns to the return yoke layer, is concentrated on the convex portion (that is, it is difficult that the magnetic flux returns to the return yoke layer to be properly dispersed) the convex portion may reach the magnetic saturation easily. In Patent Document 3 described above, because the width of the convex portion is smaller than the width of the main magnetic pole layer as shown in FIG. 5, the convex portion has a shape to reach the magnetic saturation more easily. Furthermore, in Patent Document 3, even if the convex portion is formed toward a lower side, it is very difficult to form the convex toward the lower side. In Patent Document 3, because an angle portion is formed in the convex portion, the magnetic flux leaks from the angle portion to the recording medium at the time of a nonrecording operation, thereby causing a problem such as an erasure of data recorded in the recording medium. As described above in regards to the invention of Patent Document 3, it may be impossible to suppress the generation of the PTP and avoid the reduction of the recording ability.